This invention relates to methods for automatically replenishing a fluid reservoir and to devices which perform this method, and more particularly, to the replenishing of oil in the coolant system of an electric generator. Spray oil cooled electric generators found in self-contained variable speed constant frequency (VSCF) power generating systems for aircraft contain a reservoir which provides a supply of oil for recirculation through a cooling loop. This reservoir provides a free volume for expansion of the oil and for separation of air entrained by virtue of the spray oil cooling within the generator. Present VSCF systems use a sight glass to determine the amount of oil in this reservoir. Oil is added if the level falls below the "add" mark on the glass.
Ground support equipment and crews are required to inspect and add oil. In some instances, the engines are located far above the ground and frequent inspection may be required. The level and the amount of oil in the reservoir can be influenced by such factors as shutdown time, the temperature of the oil, and the location of the engine on the aircraft, since the slope of the wing reverses with the left and right hand sides. It is therefore desirable to devise a system for adding oil to the VSCF power system reservoir automatically when required.